Formed films are used in end-products such as absorbent articles, including feminine hygiene products, adult incontinence products, and baby diapers, for example. One type of formed film that may be used in such products is a so-called topsheet, which is a top layer of the end-product that contacts the skin of the user (wearer) of the end-product. It is desirable for a topsheet that is made from a plastic film to have the visual appearance and softness of a soft cloth, instead of a stiff plastic film. However, trade-offs exist between achieving softness and a pleasant visual appearance (e.g. pattern visibility, low gloss, etc.), and the convertibility of the topsheet into the end-product, as well as the performance of the topsheet (e.g. surface distribution, wetness, masking, rewet, etc.) in the end-product when worn by the user.
The visual appearance of a topsheet, including the patterns and sizes of apertures, is generated by “thermal” forming or thermoforming, which may include vacuum-forming, hydro-forming, embossing, mechanical perforating, etc., of a web of material. In vacuum-forming and hydro-forming processes, a web is deposited on a rotating forming structure, such as a screen, that includes openings corresponding to a desired pattern. In a vacuum-forming process, a relative vacuum is established across the forming structure so that the web is drawn into the openings, thereby forming a series of protrusions on the film surface. If the vacuum differential is sufficient, an opening such as a micro-aperture, may be formed in the web at the apex of each protrusion. In a hydro-forming process, similar protrusions/micro-apertures may be formed by directing a high pressure water stream at the side of the web that is opposite the forming structure. The pressure of the water stream forces the web into the opening of the forming structure. If sufficient pressure is applied, an aperture is formed in the web at the apex of each protrusion. Apertures may also be formed using mechanical methods such as needle punching, but such methods may require additional steps to provide the three dimensionality that tends to enhance the perceived softness of the final film.
A visual appearance that is appealing to users is traditionally generated by a large hydraulic radius, which should also promote absorption, and consequently a relatively high caliper or thickness, which may make the film more difficult to convert into the final end-product. Softness may be generated by softer polymers, flexible micro-structures, and cushioning structures. However, forming the webs of materials at high temperatures may make the resulting films stiffer and less soft. Conversely, softer films tend to be more difficult to convert into the final product.
In general, topsheets that are made from plastic films have better performance characteristics when used in the end-product as compared to topsheets that are made from non-woven materials. However, a topsheet made from a plastic film may have a visual appearance that is higher in gloss and therefore may be more “plastic-looking” than a non-woven topsheet, and a plastic film topsheet may feel more “sticky” or “tacky” to the wearer than a non-woven topsheet.
Typical apertured topsheets generally create a visual appearance by thermoforming holes having round, elongated, hexagonal and/or slit shapes, but challenges exist to create a unique and effective visual appearance. On the other hand, embossed topsheets may have unique visual appearances due to the laser engraving technology that is used to generate such structures, but embossed topsheets generally have very small hydraulic radii and lower performance as compared to apertured topsheets. In addition, higher basis weights are typically needed for embossed topsheets to obtain visual appearances that are more appealing to the user.
It is desirable to create a topsheet that 1) has a unique and effective visual appearance in order to convey a promise of protection to the user, 2) delivers extraordinary softness to the user, 3) assures performance at least comparable to traditional films, and 4) is able to be converted into the end-product on conventional equipment.